The invention relates generally to a system for limiting pressure differences in dual compressor chillers.
Certain refrigeration and air conditioning systems generally rely on a chiller to reduce the temperature of a process fluid, typically water. Air may then pass over this chilled process fluid in an air handler and circulate throughout a building. In typical chillers, the process fluid is cooled by an evaporator which absorbs heat from the process fluid through evaporating refrigerant. The refrigerant may then be compressed in a compressor and transferred to a condenser. In a liquid cooled condenser, the refrigerant is generally cooled by a second process fluid, causing the refrigerant to condense into a liquid. The liquid refrigerant may then be transferred back to the evaporator, to begin another refrigeration cycle.
Refrigeration system efficiency may be improved by linking multiple chillers together in a series flow configuration. In a dual chiller series flow arrangement, for example, the evaporator process fluid is circulated in series through two chillers. This configuration allows evaporator process fluid to be cooled in two discrete increments. Warmer process fluid enters the evaporator of the first or “lead” chiller and is cooled by an initial amount. Then, the cooler process fluid enters the evaporator of the second or “lag” chiller where its temperature is further reduced. Because the process fluid entering the lead evaporator is warmer, the lead evaporator will operate at a higher pressure compared to the lag evaporator. The higher evaporator pressure reduces compressor head, resulting in greater efficiency.
To further increase efficiency, process fluid from a cooling tower may circulate through two condensers. In this configuration, cooler process fluid first enters the condenser of the lag chiller. The process fluid is heated in this condenser before flowing to the condenser of the lead chiller. This arrangement is known as a counterflow configuration of the chillers and results in greater efficiency because the lead chiller has both a higher evaporator process fluid temperature and a higher condenser process fluid temperature. The higher temperatures result in higher pressures in both the evaporator and condenser of the lead chiller, thus reducing compressor head and yielding increased efficiency.
One disadvantage of series flow chillers is that they are typically more expensive because of the additional evaporator, condenser and conduits that must be installed. In addition, multiple chillers require a large amount of space, and some facilities may not be able to accommodate them. These constraints may preclude the use of series flow chillers and force facilities to adopt less efficient single chiller systems. Therefore, it would be advantageous for a single chiller to achieve the efficiency advantage of a series flow configuration.